The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Torque-based control can be implemented for internal combustion engines to achieve a desired drive characteristic. Engine torque-based control systems interpret an accelerator pedal position of the vehicle as an engine torque request. The engine is controlled to deliver the requested engine torque to provide the desired drive characteristic.
Axle or wheel torque-based control systems, such as Coordinated Torque Control described in commonly assigned U.S. Pat. No. 7,021,282, can provide improved vehicle response. An axle torque-based control system uses the accelerator pedal position and vehicle speed to determine how much vehicle torque the driver wants in order to achieve the driver's desired acceleration. This vehicle, axle, or wheel torque command is converted to an engine torque command by dividing the axle torque by the overall powertrain transfer ratio. The overall powertrain transfer ratio is the product of the torque ratios of 1) the torque converter, 2) the transmission gearbox, 3) the final drive, and 4) the transfer case (if present).
The final drive ratio is a known fixed ratio. The transfer case (if present) has one of two known ratios (4Hi or 4Low). The gearbox torque ratio is well known when in gear and can be reasonably estimated while shifting. The torque converter torque ratio (or torque converter gain) is usually known to sufficient accuracy, except for the case when the torque converter gain is rapidly increased after returning from an overrun mode (negative slip) to normal converter mode. During this period of rapid rise in converter gain, the torque converter gain estimation can be lagging. This results in a torque bump when the driver tips in after a deceleration maneuver.